Fire polished showerhead electrode

ABSTRACT

A method for processing a quartz showerhead-type electrode having a first surface, a second surface, and a plurality of passages extending through the electrode, from the first surface to the second surface, each passage defined by a sidewall, which comprises fire polishing the sidewalls. Additionally, the sidewalls have a central portion and opposing transition areas adjacent to the first and second surfaces, and the method comprises fire polishing the transition areas. Further, the electrode may be textured after fire polishing.

FIELD OF THE INVENTION

[0001] The present invention relates to a fire polished quartz showerhead electrode.

BACKGROUND OF THE INVENTION

[0002] Plasmas are used for many processes to alter the surface of a material, such as an integrated circuit chip wafer, in a controlled manner. Typical applications include etching of semiconductor wafers, ion implantation, ion milling, and removal of material in a process known as reactive ion etching. Fabrication of an integrated circuit usually begins with a thin, polished slice or wafer of a high purity, single-crystal semiconductor material, such as silicon or germanium, which is subjected to a sequence of processing steps, such as deposition of materials on, or removing materials from, the wafer to form structured layers of the integrated circuit. Early etching techniques were based on chemical etching agents. Early deposition processes included sputtering or chemical vapor deposition techniques. More recently, etching and deposition processes based on energetic plasma ions taking place in a plasma reactor have been replacing the earlier techniques because of environmental and health concerns, in addition to an improvement in quality which results from the plasma process.

[0003] Plasma reactors typically include a chamber in which the plasma is established, a source of gas which is ionized to form the plasma, a source of energy to ionize the gas, a vacuum system to reduce the pressure within the chamber to an appropriate level for a particular process, and a means for allowing the gas to enter the chamber in a controlled manner.

[0004] Generally, an item to be processed, which may typically be a semiconductor wafer with appropriate masking, is placed within the chamber and is electrically biased relative to the gas in order to induce the charged species of the ionized gas to impinge on the wafer, preferably substantially normal to the surface. In some cases, chemically reactive gases are also used to enhance the rate of etching in a process called reactive ion etching.

[0005] In a typical plasma etching system, the chamber has an upper electrode which serves as an anode, and a lower electrode which serves as a cathode. The item to be processed is generally mounted on the cathode. In such a system, the cathode is biased negatively with respect to the anode and the chamber walls, and thereby establishes an electric field between the cathode and the surrounding region. The electric field gradient established by the negatively biased cathode is sufficiently strong to dissociate the particular gas used in the chamber, at the operating pressure, to form a plasma. The dissociated gas results in charged particles in the form of electrons and positively charged ions, each of which are accelerated by the electric field. The surface of the item to be processed is etched by the positive ions that are accelerated towards the negatively charged cathode by the electric field. It is generally important in semiconductor processing that the ions strike the wafer with a uniform flux density so that all parts of the wafer are processed at the same rate, and that the ions follow a path that is perpendicular to the surface of the wafer in order to prevent defects associated with undesirable etching of the sides of the semiconductor structures. It is also important that extraneous particles which can cause defects are eliminated.

[0006] Generally the upper electrode, the anode, is provided with gas passages in a distribution that encourages an even distribution, and uniform flow, of plasma over the surface of the item to be processed. Typically, the anode is comprised of a quartz disk of uniform thickness, and is referred to as a showerhead electrode in the art. These showerhead electrodes are often coated with a photo-resist polymer before use in a plasma etching system.

[0007] In manufacturing a showerhead electrode, the gas passages are normally formed by drilling, boring, or some other mechanical process. A disadvantage to these processing techniques is that they leave rough edges, cracks, and other such surface defects in and around the passages, which may allow tiny chips or particles of material to separate from the surface during use, known as “shedding.” This shedding most often occurs at the edges of the passages, where they meet the surface of the electrode. When shedding occurs during plasma etching, particles of electrode material can travel to the surface of the product being processed and damage the surface, thereby ruining the product.

SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to provide a method for processing a quartz showerhead-type electrode. Accordingly, the invention comprises the steps of providing a quartz plate having a first surface, a second surface, and a passage extending through the electrode, from the first surface to the second surface, the passage defined by a sidewall, and fire polishing the sidewall.

[0009] It is contemplated that the invention may further comprise the step of abrasively texturing one or more of the surfaces of the electrode.

[0010] It is also contemplated that the invention may further comprise the steps of filling the passage with wax and abrasively texturing one or more surfaces of the electrode.

[0011] It is also contemplated that the quartz plate is provided with a plurality of passages extending through the electrode, from the first surface to the second surface, each passage defined by a sidewall, and that the sidewalls are fire polished.

[0012] Additionally, the invention comprises the steps of providing a quartz plate having a first surface, a second surface, and a passage extending through the electrode, from the first surface to the second surface, the passage defined by a sidewall having a central portion and opposing transition areas adjacent to the first and second surfaces, and fire polishing the transition areas.

[0013] It is also contemplated that the quartz plate is provided with a plurality of passages extending through the electrode, from the first surface to the second surface, each passage defined by a sidewall having a central portion and opposing transition areas adjacent to the first and second surfaces, and that the transition areas are fire polished.

[0014] It is another object of the present invention to provide a method for manufacturing a quartz showerhead-type electrode. Accordingly, the invention comprises the steps of providing a quartz plate having a first surface and a second surface, creating a passage extending through the plate, from the first surface to the second surface, the passage defined by a sidewall, and fire polishing the sidewall.

[0015] It is contemplated that the invention may further comprise creating a plurality of passages extending through the plate, from the first surface to the second surface, each passage defined by a sidewall, and fire polishing the sidewalls.

[0016] Additionally, the invention comprises the steps of providing a quartz plate having a first surface and a second surface, creating a passage extending through the plate, from the first surface to the second surface, the passage defined by a sidewall having a central portion and opposing transition areas adjacent to the first and second surfaces, and fire polishing the transition areas.

[0017] It is contemplated that the invention may further comprise the steps of creating a plurality of passages extending through the plate, from the first surface to the second surface, each passage defined by a sidewall having a central portion and opposing transition areas adjacent to the first and second surfaces, and fire polishing the transition areas.

[0018] It is another object of the present invention to provide a quartz showerhead-type electrode. Accordingly, the invention comprises a quartz plate, having a first surface, a second surface, and a passage extending through the plate, from the first surface to the second surface, the passage defined by a sidewall, wherein the sidewall is fire polished.

[0019] It is contemplated that one or more surfaces of the electrode of the present invention may be textured.

[0020] It is also contemplated that the electrode of the present invention may further comprise a plurality of passages extending through the plate, from the first surface to the second surface, each passage defined by a sidewall, wherein the sidewalls are fire polished.

[0021] Additionally, the invention comprises a quartz plate, having a first surface, a second surface, and a passage extending through the plate, from the first surface to the second surface, the passage defined by a sidewall having a central portion and opposing transition areas adjacent to the first and second surfaces, wherein the transition areas are fire polished.

[0022] It is contemplated that the electrode of the present invention may further comprise a plurality of passages extending through the plate, from the first surface to the second surface, each passage defined by a sidewall having a central portion and opposing transition areas adjacent to the first and second surfaces, wherein the transition areas are fire polished.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention is described in detail below with reference to the following figures:

[0024]FIG. 1 is a top view of the showerhead electrode of the present invention;

[0025]FIG. 2 is a cross-section view of the showerhead electrode of FIG. 1 of the present invention;

[0026]FIG. 3 is a top view of a passage of the showerhead electrode of the present invention before fire polishing, magnified to show detail;

[0027]FIG. 4 is a cross-section view of the showerhead electrode of FIG. 1 of the present invention after it has been coated with a photo-resist polymer;

[0028]FIG. 5 is a cross-section view of the showerhead electrode of FIG. 1 of the present invention, after the passages have been filled with wax; and

[0029]FIG. 6 is a top view of a passage of the showerhead electrode of the present invention after it has been fire polished and textured.

DETAILED DESCRIPTION OF THE INVENTION

[0030] While this invention is susceptible of embodiment in many different forms, there is shown in the drawings, and will herein be described in detail, a preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiment illustrated.

[0031] A showerhead electrode 10 is illustrated in FIGS. 1 and 2. The electrode 10 comprises a plate 20, with a first surface 30, a second surface 32, and a plurality of passages 22. Each of the passages 22 is defined by a generally cylindrical sidewall 28, extending from the first surface 30 to the second surface 32. Each sidewall 28 is made up of a central portion 25 and opposing transition areas 24 at either end, which are adjacent to the first 30 and second surfaces 32. The dotted lines 27 in FIG. 2 illustrate approximately the boundaries between the central portion 25 and the transition areas 24. The passages 22 allow gas to flow through the electrode 10. The plate 20 is generally disk-shaped. The first and second surfaces 30, 32, respectively, are circular and are substantially flat and parallel to each other. The passages 22 are cylindrical in shape and are arranged in a pattern of concentric circles, making them evenly dispersed on the electrode 10. The passages 22 are typically 0.010 inches to 0.030 inches in diameter.

[0032] The electrode 10 is made as follows. A disk-shaped quartz plate 20 is provided, having a first surface 30 and a second surface 32. A plurality of passages 22 are created, extending from the first surface 30 to the second surface 32. The passages 22 may be created ultrasonically or by using a water jet, a laser, or a drill, such as with a diamond bit.

[0033] The electrode 10 is fire polished, most importantly at the transition areas 24, to prevent shedding. Fire polishing prevents shedding by eliminating chips or cracks in the electrode 10 that may allow shedding to occur. These chips and cracks exist primarily in the rough edges of the transition areas 24, which can be seen in detail in FIG. 3. Fire polishing comprises heating a material until its surface begins to soften and flow, and then allowing it to cool, leaving a smooth surface. When the electrode 10 is fire polished, the surface 30, 32 becomes smooth. Additionally, the transition areas 24 become smooth and curved, as shown in FIG. 2. This is believed to occur because surface tension in the flowing quartz causes the material at the transition areas 24 to develop a small radius, which remains after the material re-solidifies. The smooth, curved surfaces of the fire polished transition areas 24 are not prone to shedding. When the sidewalls 28 of the passages 22 are fire polished, they become smooth as well.

[0034] A quartz electrode 10 may be fire polished by exposing it to a hydrogen/oxygen flame until the surface reaches a temperature of approximately 1700° C., and then allowing it to cool. Alternatively, fire polishing may be done locally around the transition areas 24 by using a laser as the heat source. Fire polishing may be utilized as a step in manufacturing a new electrode or as a method of repairing a previously-used electrode, and the present invention encompasses both. Suitable fire polishing of quartz electrodes may be performed by Technical Glass Products, Inc. of Painesville Twp., Ohio.

[0035] After the electrode 10 has been fire polished, the surfaces 30, 32 are textured. Texturing the surfaces 30, 32 of the electrode 10 is done by sand blasting or grit blasting with 320 grit aluminum oxide (Al₂O₃) at low pressure. The rough surface created by texturing improves adherence of a photo-resist polymer coating 34, which may later be applied to the surfaces 30, 32 of the electrode 10, as shown in FIG. 4. Alternatively, as seen in FIG. 5, the passages 22 may be filled with wax 26 before texturing, which acts to protect the sidewalls 28 and/or the transition areas 24 from damage during the texturing process. After texturing is complete, the wax 26 is removed by applying heat to melt the wax 26 away or by using a solvent to dissolve the wax 26.

[0036] The electrode 10 is annealed after fire polishing. Annealing relieves residual stresses within the electrode material that may be created by fire polishing. A quartz showerhead electrode 10 is annealed by heating the electrode 10 to approximately 1140° C., holding at that temperature for approximately 3 hours, and allowing the electrode 10 to cool in the oven overnight, rather than removing it to cool. Suitable annealing of quartz electrodes may also be performed by Technical Glass Products, Inc.

[0037] After the electrode 10 has been manufactured, fire polished, annealed, and textured, the product is a quartz showerhead electrode 10, as illustrated in FIGS. 1 and 2, having a textured surface and smooth, curved transition areas 24. The textured surface and smooth, curved transition areas 24 of such an electrode may be seen in detail in FIG. 6.

[0038] While specific embodiments of the invention have been illustrated and described herein, numerous modifications come to mind without significantly departing from the spirit of the invention and the scope of protection is only limited by the scope of the accompanying Claims. 

I claim:
 1. A method for processing a quartz showerhead-type electrode comprising the steps of: providing a quartz plate having a first surface, a second surface, and a passage extending through the electrode, from the first surface to the second surface, the passage defined by a sidewall; and fire polishing the sidewall.
 2. The method of claim 1, further comprising the step of abrasively texturing one of the surfaces of the electrode.
 3. The method of claim 1, further comprising the steps of: filling the passage with wax; and abrasively texturing one of the surfaces of the electrode.
 4. The method of claim 1, wherein the quartz plate is provided with a plurality of passages extending through the electrode, from the first surface to the second surface, each passage defined by a sidewall, further comprising fire polishing the sidewalls.
 5. The method of claim 4, further comprising the step of abrasively texturing one of the surfaces of the electrode.
 6. The method of claim 4, further comprising the steps of: filling the passages with wax; and abrasively texturing one of the surfaces of the electrode.
 7. A method for manufacturing a quartz showerhead-type electrode, comprising the steps of: providing a quartz plate having a first surface and a second surface; creating a passage extending through the plate, from the first surface to the second surface, the passage defined by a sidewall; and fire polishing the sidewall.
 8. The method of claim 7, further comprising the step of abrasively texturing one of the surfaces of the plate.
 9. The method of claim 7, further comprising the steps of: filling the passage with wax; and abrasively texturing one of the surfaces of the plate.
 10. The method of claim 7, further comprising the steps of: creating a plurality of passages extending through the plate, from the first surface to the second surface, each passage defined by a sidewall; and fire polishing the sidewalls.
 11. The method of claim 10, further comprising the step of abrasively texturing one of the surfaces of the plate.
 12. The method of claim 10, further comprising the steps of: filling the passages with wax; and abrasively texturing one of the surfaces of the plate.
 13. A quartz showerhead-type electrode, comprising: a quartz plate, having a first surface and a second surface; and a passage extending through the plate, from the first surface to the second surface, the passage defined by a sidewall; wherein the sidewall is fire polished.
 14. The electrode of claim 13, wherein one of the surfaces of the electrode is textured.
 15. The electrode of claim 13, further comprising: a plurality of passages extending through the plate, from the first surface to the second surface, each passage defined by a sidewall; wherein the sidewalls are fire polished.
 16. The electrode of claim 15, wherein one of the surfaces of the electrode is textured.
 17. A method for processing a quartz showerhead-type electrode comprising the steps of: providing a quartz plate having a first surface, a second surface, and a passage extending through the electrode, from the first surface to the second surface, the passage defined by a sidewall having a central portion and opposing transition areas adjacent to the first and second surfaces; and fire polishing the transition areas.
 18. The method of claim 17, further comprising the step of abrasively texturing one of the surfaces of the electrode.
 19. The method of claim 17, further comprising the steps of: filling the passage with wax; and abrasively texturing one of the surfaces of the electrode.
 20. The method of claim 17, wherein the quartz plate is provided with a plurality of passages extending through the electrode, from the first surface to the second surface, each passage defined by a sidewall having a central portion and opposing transition areas adjacent to the first and second surfaces, further comprising fire polishing the transition areas.
 21. The method of claim 20, further comprising the step of abrasively texturing one of the surfaces of the electrode.
 22. The method of claim 20, further comprising the steps of: filling the passages with wax; and abrasively texturing one of the surfaces of the electrode.
 23. A method for manufacturing a quartz showerhead-type electrode, comprising the steps of: providing a quartz plate having a first surface and a second surface; creating a passage extending through the plate, from the first surface to the second surface, the passage defined by a sidewall having a central portion and opposing transition areas adjacent to the first and second surfaces; and fire polishing the transition areas.
 24. The method of claim 23, further comprising the step of abrasively texturing one of the surfaces of the plate.
 25. The method of claim 23, further comprising the steps of: filling the passage with wax; and abrasively texturing one of the surfaces of the plate.
 26. The method of claim 23, further comprising the steps of: creating a plurality of passages extending through the plate, from the first surface to the second surface, each passage defined by a sidewall having a central portion and opposing transition areas adjacent to the first and second surfaces; and fire polishing the transition areas.
 27. The method of claim 26, further comprising the step of abrasively texturing one of the surfaces of the plate.
 28. The method of claim 26, further comprising the steps of: filling the passages with wax; and abrasively texturing one of the surfaces of the plate.
 29. A quartz showerhead-type electrode, comprising: a quartz plate, having a first surface and a second surface; and a passage extending through the plate, from the first surface to the second surface, the passage defined by a sidewall having a central portion and opposing transition areas adjacent to the first and second surfaces; wherein the transition areas are fire polished.
 30. The electrode of claim 29, wherein the transition areas are substantially smooth and curved.
 31. The electrode of claim 29, wherein one of the surfaces of the electrode is textured.
 32. The electrode of claim 29, further comprising a plurality of passages extending through the plate, from the first surface to the second surface, each passage defined by a sidewall having a central portion and opposing transition areas adjacent to the first and second surfaces; wherein the transition areas are fire polished.
 33. The electrode of claim 32, wherein the transition areas are substantially smooth and curved.
 34. The electrode of claim 32, wherein one of the surfaces of the electrode is textured. 